The present invention relates generally to chargers for energy storage systems, and more specifically, but not exclusively, to improvements in universal input charger efficiency.
Chargers for plug-in electric vehicles convert AC input voltage to an appropriate DC charging voltage applied to the energy storage system. Efficiencies in the charging process are particularly important because of the relatively large amounts of energy transferred and stored during the frequent charging cycles. Those responsible for charging systems and methods are always looking for ways to improve charging efficiency.
One fundamental charger design includes two stages, a boost stage and an isolation stage. The boost stage provides a power factor correction front end that is required of all commercial charging systems for electric vehicles. The isolation stage provides isolation of the energy storage system from the AC input line and a buck output. The isolation removes any common mode currents that would be present in the case that the isolation was not present, and the buck component allows the energy storage system to be at a much lower voltage than the boost output stage. For example, assume that the efficiency of the boost stage is around M % and the efficiency of the isolation stage is around N %, there is a total efficiency of P %, where P is less than both M and N because M and N are each less than 1.
What is needed is an improved charger and charging method that improves charging efficiency.